The term plywood refers to a whole family of engineered wood products, largely used in the construction of homes and buildings. However, the various types of plywood have found their way into many other products, including furniture, handicrafts and industrial uses. Specialized plywood products have been developed for a wide variety of applications.
One of the ways that plywood is used in architecture is for subflooring. Per building code, most residences have ¾” thick plywood or OSB installed as the subfloor. While both have a similar overall strength, OSB is more prone to absorbing moisture along the edges and can be more easily broken by impact. Nevertheless, OSB is commonly used for flooring and sheathing on homes, due to its lower cost, when compared to construction-grade softwood plywood.
When plywood is used for subflooring, most people cover the plywood floor with carpet or vinyl flooring (linoleum). Ceramic tile can be used as well, although that is not our concern at this moment. Wall to wall carpet or flooring on plywood is often installed using glue or some adhesive to ensure that it remains in its place. The glue does its job pretty well but when it is time to replace the carpet or change the type of flooring, the task of removing carpet glue from plywood becomes a nightmare.
The first difficult task in this whole exercise is removing the carpet or flooring. If it is carpeting, it can usually be ripped out, peeling it from the plywood floor. Once you have completely removed the carpet from the floor, there will still be remnants of glue remaining. If it is yellow colored glue, it is the more traditional type. But if it is brown or tan colored glue, it is tar based glue.
Removing vinyl flooring can be more challenging, as the flooring will not peel off, like carpeting will. Rather, it will have to be scraped off the floor. This can be good, with self-stick vinyl tiles, which tend to peel off intact, complete with their adhesive. But in the case of roll flooring, chances are highly likely that it will come off in a lot of small pieces and may not bring the glue up with it.
The big question is how important it is that the floor be smooth before new flooring is installed. If carpeting over the pad is being installed without adhesive, it may not be necessary to remove all the adhesive. But just about any other type of flooring will require a smooth surface.
Scrape the Glue
Scraping of the glue is the least costly method of removing carpet glue, as you can do it without having to rent any expensive equipment. However, it is also the hardest way of removing the adhesive and making the floor smooth again.
The first step of this method is to make the glue softer so it can be easily worked around with. A number of solvents can do the job of softening the glue including paint thinners, turpentine, water and mineral spirits. All these chemicals work by tearing down the enzymes found in the glue, easing the task of removing the glue from the plywood subfloor. Different solvents work better on different types of glues so if you know the type of glue on your floor you can do the task much more easily.
While using these solvents, you should use the appropriate personal safety equipment, to include gloves and goggles. All of them are capable of causing skin irritations, but are even more dangerous if they get in the eye.
These solvents should only be applied once the carpeting or vinyl has been removed. Carpeting will soak up the solvents and vinyl flooring will resist it. In both cases, that prevents the solvent from reaching the adhesive it needs to soften.
Once you have ensured that the entire surface of the glue has been sprayed with the solvent, wait about half an hour, allowing the solvent to soften the glue, making it ready to remove. Once softened, you can use a hand scraper, a putty knife or a floor scraper to tear away and wipe off all the glue from the floor. Make sure that you are thorough so that no glue is left on the floor.
Please note that you may have to reapply solvent on the floor, if it evaporates before you can get to all areas. The purpose of the solvent is to soften the glue; but it will only remain soft as long as it is wet. Should the glue begin to dry, you’ll want to apply more solvent.
Sanding Glue from Plywood Floors
The use of mineral spirits and thinners to remove glue from plywood works best for floors which are smaller in size, due to the problem of the solvent drying before the scraping is done. If you have to remove glue from a larger area, sanding is a more preferable option. Sanding requires less time and labor in comparison to scraping.
The process of sanding generates heat, which helps by making the glue softer, as well as the abrasive action of the sandpaper scraping the glue and breaking it down. However, too much heat can be a problem, as it will gum up the sandpaper. Ideally, you don’t want that, because it will add to your cost.
Unless you are sanding a very small area, you’re going to want to rent a flooring sander for this project. These come in two types, belt sanders and vibratory sanders. The belt type is much faster to use, but carries the risk of oversanding. It’s very easy to gouge your plywood subfloor, creating areas that will need to be puttied and sanded in order to have a smooth floor once again.
In addition to whatever flooring sander you use, you will probably also want a smaller sander for working around edges and in difficult to reach areas. A handheld belt sander is usually the best for this, as it will remove the glue faster than either a disk sander or palm sander. While those other types of sanders can be used, they are best left for finishing work.
Before sanding, inspect the floor for nails or screws which are sticking out above the floor surface. Drive them in, if possible or remove and replace them. You should never remove flooring nails or screws without replacing them, as it can leave the floor loose in that spot, leading to squeaky floors.
As you are sanding the floor, stop from time to time to sweep up or vacuum up the sanding dust. When too much dust builds up, it’s hard to tell what parts are sanded and what parts still need work. It can also be helpful to work in sections, dividing the floor up and finishing one area, before moving on to the next.
Covering the Subfloor with Underlayment
Removing the glue from a floor may not be the best option for you, especially if doing so will cause damage to the subfloor. Rather than risk that, you may want to consider installing underlayment over the existing subfloor and glue, to provide you with a smooth surface for your new flooring. This is a more expensive, but quicker option, especially when there is a lot of glue to deal with.
This is not to say that you won’t have to deal with any glue whatsoever, if you use underlayment. But the only glue you will need to deal with are high points, where there was too much glue applied. In those cases, a quick hit with a belt sander, bringing that high point down to the level of the rest of the glue, is usually sufficient.
Luan plywood is normally used for underlayment, due to it being thin and providing a smooth finish. Before attaching your underlayment, lay the individual pieces out on the subfloor and check to see that adjacent edges are level. If not, you may need to sand off some high points under one of the sheets.
It is a good idea to use construction adhesive, as well as flooring nails, for installing the underlayment. The addition of a thin layer of construction adhesive helps to reduce the risk of the new underlayment squeaking from movement. It essentially ensures that the underlayment and the subfloor stay in the same place, as compared to one another. However, never try using just construction adhesive, without flooring nails, for installing underlayment.
Depending on the condition of your subfloor, how well you install your underlayment and the type of flooring you’re going to put on top of it, you may need to putty the seams and sand them. This is especially true if you are installing any sort of vinyl flooring. High edges or gaps between sheets can cause serious damage to vinyl flooring, eventually causing it to crack. Always be sure to sand these puttied edges smooth, so as to not create another problem. But this sanding can be done with a simple palm sander.